1. Field of the Invention
The present invention relates to an image pickup device such as a digital still camera provided with a blur processing function and a method for controlling the image pickup device.
2. Description of the Related Art
An image pickup element used in a compact digital camera is smaller both than an image pickup element used in a single-lens reflex camera and a silver-salt film. Therefore, in order to photograph an image with the same view angle, the focal length of a photographic optical system is required to be shorter. Even if the F-number of the photographic optical system is set the same, when the focal length is small, the depth of field becomes greater. Although the depth of field may become shallow when the F-number can be reduced in proportion to a shortening of the focal length, an aperture of the photographic optical system would be required to be large, which incurs an increase in both the size and cost of the photographic optical system. Therefore, comparatively speaking, the in-focus range is wider when photographing with such a compact digital camera. In this respect, it can be considered as an advantage of the compact digital camera when photographing an image with the same brightness. However, it can also be disadvantageous when photographing an image such as a portrait for which the blurring degree of the background is important, because even the background of the image is undesirably clear. In order to solve the above-mentioned problem, cameras to blur the background of the image via image processing have been proposed in Japanese Application Publication Number 2000-207549, Japanese Application Publication Number 2000-259823, Japanese Application Publication Number 2005-175956 and Japanese Application Publication Number Hei9-318870.
It is known that distance information corresponding to respective areas within the image is indispensable in order to properly determine an area whereto blur processing is performed with an appropriate blurring amount. However, in the aforementioned proposals, acquisition of the essential information of distance lacks explicitness in description. More disadvantageously, an adoption of optical systems composed of image pickup elements of two systems has caused the problems of increased size and cost of the optical systems. Furthermore, in the aforementioned proposals, since there is no consideration of determining the proper blurring amount prior to a user's photographing, which amounts to an intended adjustment, an actual minor adjustment, expressed as an addition of a blurring effect, has not been feasible in reality.